The actions of neurotrophins on the survival of trigeminal sensory neurons during development is now well established. Previous studies using neurotrophin null mutant and transgenic mice have added to our understanding of neurotrophins. However, lethality and poor control of promoter-driven neurotrophin expression in these models has made it impossible to characterize alternative actions of neurotrophins on trigeminal sensory neurons. The role of this Core is to generate transgene models in which neurotrophin expression can be induced in peripheral or central targets of trigeminal sensory neurons during specified periods. This Core will utilize target specific promoters in combination with the newly developed RevTet-On system (Clonetech) to induce the over-expression of NGF, NT-3 and BDNF in trigeminally-relevant target tissues. The RevTet-On system employs a two construct system which yields two transgenic mouse lines that when bred together, generate "bigenic" mice with target- specific transgene expression induced by tetracycline administration. Some Projects requ7ire mice that over-express nerve growth factor (NGF), neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF) in skin (NGF, NT-3), facial skeletal muscle (NT-3) and brainstem/cortex (NGF, NT-3, and BDNF). Core B will generate and inject specified transgene constructs, and then characterized founder mice to identify the suitable lines. Core B will breed mouse lines to generate bigenic mice. Regulated neurotrophin transgene expression will be evaluated at mRNA and protein levels and mice will be made available. The advantage of this approach is that the actions of neurotrophins can be studied in vivo at defined stages in the absence of the complicating effects of neurotrophin-regulated trigeminal survival. Also, craniofacial tissues can be placed in culture and neurotrophin synthesis can be induce din endogenous target tissues. Results from mice generated by this Core will provide new biological information about neurotrophic can reveal now manipulation of the trophic support of neurons will be useful to treat pathologic neural conditions involving craniofacial sensory systems.